Image-guidance radiation therapy (IGRT) systems are now widely available and implemented for routine clinical use in many clinics, in large part due to their tight integration with medical linear accelerators and treatment planning systems (TPS). Increased geometric precision and accuracy are now widely achievable in radiotherapy delivery because users can correct patient translations and rotations immediately prior to administration of radiotherapy by registering IGRT ‘images of the day’ to those initially used for treatment planning. Furthermore, comparison of successive daily IGRT images can help to quantify changes of internal anatomy throughout the course of therapy. However, introducing image guidance within busy radiation therapy clinics requires thoughtful commissioning and quality control (QC) protocols, and judicious modification of existing radiation therapy processes and protocols. While the uses of such novel systems will continue to evolve, their performance must be diligently maintained at the highest level, as they will be relied upon to insure accuracy in the treatment delivery process. In fact, such systems may be used to justify PTV margin reduction, thus further emphasizing the need for accuracy and precision through careful QC.

There are two key features of IGRT systems that require particular attention: geometric accuracy and image quality. First, as a separate modality, the chosen IGRT system possesses its own reference origin and coordinate system, which in some cases may not be physically coincident with that of the megavoltage treatment beam or the medical linear accelerator isocenter. Therefore, the geometric relationship between the IGRT dataset and the megavoltage treatment beam must be established and monitored to ensure adequate localization, coincidence, orientation, and scaling. Second, image quality ultimately determines the ability of the IGRT system to consistently produce images capable of localizing the structures of interest, through either manual or automatic registration. Careful and continual monitoring of image quality must be performed to ensure consistent and accurate Image Guidance results. Details of a QC program for various IGRT solutions will be highlighted based on the following reports:

Learning Objectives:1. To present IGRT technologies covered by the referenced Task Groups and major considerations for their use2. To describe principles for quality control of IGRT systems3. To characterize and discuss the impact of IGRT on quality and safety of radiation therapy